1. Field of the Invention
The present invention relates to an active suspension in a vehicle such as an automobile, and more particularly to a fluid pressure type active suspension in a vehicle having a four wheel steering means.
2. Description of the Prior Art
A four wheel steering means responsive to vehicle speed so as to change the steering angle according to the vehicle speed is known as shown in, for example, Japanese Patent Laying-open Publication 60-135368. A four wheel steering means responsive to the steering angle so as to change the front to rear wheel steering angle ratio is known as shown in, for example, Japanese Patent Laying-open Publication 55-91458. By employing such a four wheel steering means the turning performance of the vehicle with a small turning radius at low vehicle speed or the steering stability of the vehicle at medium to high vehicle speed is improved.
Further, as shown in, for example, Japanese Patent Laying-open Publication 63-279915, it is known to incorporate in a vehicle such as an automobile an active suspension which comprises fluid pressure type actuators, a fluid pressure type actuator being provided between a vehicle body and each wheel, working fluid supply and exhaust means for supplying and exhausting a working fluid to and from said actuators, and a control means for controlling said working fluid supply and exhaust means according to the steering state of the vehicle so as positively to suppress the rolling of the vehicle body.
As the rolling of the vehicle body is effectively suppressed by such a fluid pressure type active suspension, it is contemplated to use it in a vehicle having a four wheel steering means so as further to improve the steering stability of the vehicle.
However, since the responsiveness of the vehicle body to the lateral acceleration in the vehicle having the four wheel steering means changes according to change of the front to rear wheel steering angle ratio, when the working fluid supply and exhaust means is controlled only in accordance with the steering state of the vehicle, it sometimes happens that the roll control for the vehicle body is too much while it sometimes happens that the roll control for the vehicle body is not enough, thus making it difficult to carry out the roll control for the vehicle body constantly at a most desirable condition.